1. Field of the Invention
The present invention relates generally to aerosol generation. More specifically, the present invention relates to an aerosol generator which provides controlled doses of medicament to a patient during use.
2. Description of Related Art
Metered dose inhalers for delivering aerosol medication for inhalation by a patient are disclosed in U.S. Pat. Nos. 5,487,378; 5,522,378; 5,622,162; 5,794,612; 5,839,430; 5,894,841; and 6,152,130. Some inhalers use the propulsive force of a propellant system such as a mixture of liquified chlorofluorocarbons. Other inhalers use an ultrasonic nebulizer system to atomize a liquid in a carrier gas stream or a burst of inspired air to fluidize and draw a dose of powder into the bronchial tract. Commonly owned U.S. Pat. Nos. 5,743,251 and 6,234,167 disclose aerosol generators wherein a liquid formulation is vaporized to form an inhalation aerosol.
In order to trigger delivery of aerosol from an inhaler, various types of breath actuation systems have been proposed. According to U.S. Pat. No. 5,622,162, some breath actuation systems require a patient's inspiratory effort to move a mechanical lever or the detected flow to rise above a preset threshold. A problem with such systems is that inspiration varies from person to person and some patients are unable to generate sufficient flow to activate the unit. Although attempts have been made to improve breath actuation systems, detection is still based on air flow generated by the patient with the result that the patient inhales a volume of air before delivery of the aerosol occurs. As a result, the patient may not inhale a full dose of medication.
Other techniques are known for generating aerosols. For example, U.S. Pat. Nos. 4,811,731 and 4,627,432 disclose devices for administering medicaments to patients in which a capsule is pierced by a pin to release a medicament in powder form. A user then inhales the released medicament through an opening in the device.